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Voltage Drop across 1N5817 Diode

Discussion in 'Electronic Basics' started by Hans Maier, Apr 5, 2004.

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  1. Hans Maier

    Hans Maier Guest

    I use a 1N5817 Schottky Diode in my circuit.
    According to the datasheed its forward voltage
    drop should be around 0.3-0.4 V

    But when i measure the voltage drop in my circuit
    it is almost 1 V at 200 mA.

    Did they send wrong diodes to me or am I missing
    something ?

    I need a diode which has a VERY low voltage drop
    @about 200mA.
     
  2. That sure sounds like a different diode. A 1N4148, perhaps.

    How much reverse voltage capability do you need and how much reverse
    current can you tolerate?. There are some very low voltage Schottkys
    that have exceptionally low forward drop.
     
  3. Hans Maier

    Hans Maier Guest

    That sure sounds like a different diode. A 1N4148, perhaps.
    Thanks, I will order new ones from a different supplier.
    I actually don't care about reverse current as long as it
    is still a diode :)

    The diode has to block 5V DC and it shouldn't drop any voltage
    in the other direction (idealy)... speed is not important at all.

    200-300 mA should be no problem for the diode ...
     
  4. If you can use surface mount parts, International Rectifier makes a 1
    amp 15 volt SMB unit that drops .34 volts at 1 amp, just over .2 volt
    at 200 ma.
    http://www.irf.com/product-info/datasheets/data/10bq15.pdf

    Here is the datasheet for the 1N5817 that shows the expected forward
    drop at 200 ma of .25 volts.
    http://www.diodes.com/datasheets/ds23001.pdf
     
  5. Hans Maier

    Hans Maier Guest

    No, SMD is currently not an option for me.
    Thanks, I hope the next diodes I get will really be 1N5817 :)
     
  6. Neil Koozer

    Neil Koozer Guest

    It's possible to get fooled with these Schottky things. If you're using
    them as rectifiers in a transformer circuit, you have to remember that the
    current is in the form of short pulses of much higher current than the
    average current. In order to get the expected voltage drop in the
    rectifier, you have to base it on the peak current. Average cuarrent is ok
    when thinking about power dissipation in the device.

    Neil
     
  7. Hans Maier

    Hans Maier Guest

    Thanks Neil,

    but its only used to prevent current flow from one circuit area
    to another but allow it in the other direction. Absolutely rock
    stable DC.
     
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